Prince Guillaume, Hereditary Grand Duke of Luxembourg (given names: Guillaume Jean Joseph Marie; born 11 November 1981), has been heir apparent to the crown of Luxembourg since his father's accession in 2000.

Guillaume has been heir apparent to the crown of Luxembourg since his father's accession in 2000. If he succeeds to the grand ducal throne, he will reign as the fifth of his name, Guillaume (English: William) V. He has been honorary chairman of the Board of Economic Development of Luxembourg since 2001. He was formerly active with the Kraizberg Foundation, a charitable institution for the disabled.[1]

At the occasion of his 30th birthday, he gave interviews during which stated that he was in a relationship with a "dear miss" that had been going strong for more than a year but insisted that they need some more time to evaluate their possible future. On 26 April 2012, the court announced the engagement of the Hereditary Grand Duke to the Belgian Countess Stéphanie de Lannoy.[4] Guillaume and Stéphanie share a common descent from Charles Marie, Prince & 5th Duke d’Arenberg, which means that Guillaume's father and Stéphanie are 7th cousins; thus Guillaume is Stéphanie's 7th cousin once removed.

The civil wedding took place on Friday, 19 October 2012; the religious wedding took place on Saturday, 20 October 2012 at the Notre-Dame Cathedral.[5]

Hereditary Grand Duke Guillaume and Hereditary Grand Duchess Stéphanie will move to London later this year 2018.[6]

Guillaume is interested in music and sports; he plays the piano and enjoys football, swimming and volleyball. He speaks Luxembourgish, French, German, Spanish and English. He regularly represents his parents in many foreign activities.[1]

Guillaume's patriline is the line from which he is descended father to son.

Patrilineal descent is the principle behind membership in royal houses, as it can be traced back through the generations - which means that if Prince Guillaume were to choose an historically accurate house name it would be Robert, as all his male-line ancestors have been of that house.

Guillaume's patriline is the line from which he is descended father to son. It follows the Dukes of Parma as well as the Kings of Spain, France, and Navarre. The line can be traced back more than 1,200 years from Robert of Hesbaye to the present day, through Kings of France & Navarre, Spain and Two-Sicilies, Dukes of Parma and Grand-Dukes of Luxembourg, Princes of Orléans and Emperors of Brazil. It is one of the oldest in Europe.

Guillaume's patriline is the line from which he is descended father to son.

^In 1986, Grand Duke Jean renounced the title Prince/Princesse de Bourbon de Parme for himself and his family, when his eldest son, then-Hereditary Grand Duke Henri married Maria-Theresa Mestre. The reason for this was that the Duke of Parma, Carlos Hugo, ruled the marriage unequal in 1981, as well as the marriage of Prince Jean to Hélène Suzanna Vestur in 1987, for which he had renounced his rights to Luxembourger throne in 1986.

^The Arrêté Grand-Ducal of 21 Septembre 1995 established that the title of Prince/Princesse de Luxembourg is reserved for the children of the sovereign and the heir to the throne. It also stated that the descendants in male lineage of the sovereign should be styled as Prince/Princesse de Nassau with qualification of Altesse Royale.

^Slovak republic website, State honoursArchived 13 April 2016 at the Wayback Machine. (click on "Holders of the Order of the 2nd Class White Double Cross" to see the holders' table) : 2nd Class received by Hereditary Grand-Duke in 2005, i.e. during the state visitArchived 24 May 2011 at the Wayback Machine. (French) of Grand-Duke, Grand-Duchess & Hereditary Grand-Duke in Slovakia (7 September 2005).